Suggestions for fog?
If you want these curvy shapes you can try Volume Empty object with two volume modifiers.

Add a Cube, switch to Sculpt mode and with enabled Dyntopo use Snake Hook tool
Add Volume &gt; Empty object
Add modifier Mesh to Volume and use the Cube as Object
Alternatively for more distortion you can use Volume Displace modifier with Cloud texture

Sculpted - three drags with Snake Hook tool (screen from edit mode)

Volume &gt; Empty object with Mesh to Volume modifier

Added Volume Displace modifier &gt; Cloud texture

... another example smaller size texture and higher Density set in shader

Volume modifier available from Blender 2.92 and above ... I'm so big fan of this feature.
Just a few clicks :)
BTW - ad to &quot;graine&quot; render - in Properties editor under Render property &gt;Sampling &gt; Denoising enable Viewport / Render Screens above are just result of 4 samples :)